Embodiments of the present invention disclose a service transmission method and a device and a system for implementing the method. The method includes: recognizing a type of a received client service, encapsulating an OTN service, and generating an OTN signal frame or a lower order ODU; querying a tag forwarding base to acquire forwarding information of the OTN signal frame or the lower order ODU; acquiring tag information, and inserting the tag information into an overhead of the OTN signal frame or the lower order ODU; and forwarding the OTN signal frame according to the forwarding information. The method may further include: receiving the OTN signal frame sent by an upstream node, extracting the tag information from the overhead of the OTN signal frame; querying the tag forwarding base according to the tag information, acquiring the forwarding information of the OTN signal frame; and forwarding the OTN signal frame to a downstream node according to the forwarding information. An OTN technology is adopted in both forwarding and transmission of the service. Therefore, in the embodiments of the present invention, the forwarding and the transmission of the service may be performed in an OTN plane only, thereby reducing hardware modules of an MPLS plane.